I could finally get into Diamond in Season 4 and I would like to share some hints that helped me in it.
Maybe some of these will be common sense or no brainer for you, but do you follow all of these in every single game?

1.Play less champions in ranked games

2.DO NOT go for full hp bursts in your laning phase

3.If your ally did something well, let him/her know it

4.Do not surrender in your games, the only exception is if you have ABSOLUTELY 0 chance to win the game

5.Never, ever focus on winning arguments, changing or bashing others

6.Focus on pushing lanes and taking objectives (turrets, inhibitors, dragon, Baron)

7.​Stop finding excuses why you cannot go up in Tiers and Divisions

8.Do not try new and strange builds in ranked games

9.Focus only on the game, no Facebook, no Youtube, no LoL Mini Games, etc. Play the game and do the rest in queue or before the game or after you finished it.

10.OVERKILL the **** out of them. Aim for more damage and not the enemies' exact health.

11.DO NOT Overestimate the power of counterpicks. Your main is alwas better than a champion you can't play, even if it's the counter of the enemy.

Detailed explanations for each points

I wish you a great Season 5,
Cheers